1. Field of the Invention
The present invention relates generally to a metal-wire working process, and more particulary to a roll-forming apparatus that reduces a wire stock into a smaller-diameter shape through the roll-forming process.
2. Description of the Prior Art
The conventional working process for a metal rod such as a metal wire stock, through which it is reduced to a smaller diameter or cross section, usually consists of roll-forming the wire stock into a diameter of 6 mm (for some special applications, 3 mm), followed by drawing such reduced-diameter wire into a further smaller diameter by plastic working. It is known that this plastic-working process includes two different methods, i.e., forming by force of pressure and elongation by drawing. Which of the two is used depends upon the type and/or property of the stock to be worked. For the pastic-working of a stock which has a relatively easy-to-break or fragile material property, the forming by force of pressure is primarily employed, and for a stock of material that is easy to elongate, the drawing process is primarily employed. For the drawing process, it may involve using an apertured die or using a roller die. It is known that the drawing process can occur more easily and more effectively by using the roller die than by using the apertured die (as disclosed in Japanese patent application as published under No. 58 (1983)-17686, for example).
As described, the forming by force of pressure and the drawing process have their own features and merits, and the drawing process involving the use of the roller die in particular provides a higher working efficiency.
For the drawing process, however, a preparatory step is required during which a wire stock to be drawn must pass through a series of roller dies prior to the actual drawing process, which requires the corresponding amount of time. Also, the drawing process has a reduction breakage limit. Because of this limit, the reduction (rate of decreasing cross section) through a single pass must usually be limited to 30% to 40%.
The roller-dies drawing process is not adequate for fragile material stock, which is difficult to work by using the roller dies and should rather be drawn by force of pressure. However, the prior art roller dies such as those mentioned earlier have a construction that does not allow the roller dies to be coupled with the driving power source, and cannot be used for drawing by force of pressure. Furthermore, it has the reduction limit as described above, and requires more passes until a final desired diameter (or cross section) can be obtained.
Although the conventional drawing processes as mentioned above may be capable of roll-forming a thin wire stock (such as from 2 mm to 0.5 mm, for example), they cannot be used for a wire stock of a smaller diameter (such as from 0.5 mm to 0.15 mm).
The roll-forming process requires that 1 as the diameter (or cross section) of a particular wire stock to be roll-formed becomes smaller, the rollers must have smaller diameters. When the smaller-diameter rollers are used, the roll-forming process must occur at a slower rate for a given number of rotations of the motor for powering those rollers.
In roll-forming those very thin wire stocks, it may be suggested that the input (driving) rollers have the same diameter (which ensures that all input rollers run with the same efficiency when the motor rotates at a fixed speed), and the follower (driven) rollers be varied in diameter for each different-diameter wire stock to be roll-formed. In this case, however, it would be necessary to provide individual roller shafts of different diameters for the corresponding different-diameter follower rollers. Whenever the follower rollers of a given diameter are changed, the roller shafts must also be changed. This problem remains yet to be solved.
In most cases where a particular wire stock is to be roll-formed into a wire of reduced diameter or cross section, it is usual to develop a reduction plan as shown in the table 1, and this reduction planning may be provided by assuming a plane of square cross section and by calculating the involved parameter values so that the final desired shape of a given wire stock can be progressively approximated to the polygonal shape such as an octagon, beginning with that square cross section (FIG. 7). An example of those parameter values thus obtained is given in Table 1. It has already been described that for the thin wire stock to be roll-formed, the smaller-diameter rollers can provide the smaller-diameter wire.
TABLE 1 ______________________________________ PASS NO. W mm H mm Am/m2 b .PHI.size ______________________________________ 1 2.394 0.898 2.67 1.693 1.844 2 2.221 0.833 2.323 1.571 1.7198 3 2.072 0.777 2.021 1.465 1.6042 4 1.932 0.724 1.758 1.366 1.496 5 1.802 0.675 1.529 1.274 1.395 6 1.681 0.630 1.330 1.188 1.301 7 1.567 0.587 1.157 1.108 1.213 8 1.462 0.548 1.007 1.034 1.132 9 1.364 0.511 0.876 0.964 1.056 10 1.272 0.477 0.762 0.899 0.984 11 1.186 0.455 0.663 0.839 0.918 12 1.107 0.415 0.577 0.782 0.857 13 1.032 0.387 0.502 0.730 0.799 14 0.962 0.360 0.436 0.680 0.745 15 0.898 0.336 0.380 0.635 0.695 16 0.837 0.314 0.330 0.592 0.548 ______________________________________